1. Field of the Invention
The present invention relates in general to radio communication systems for wireless networks. More particularly, the invention is directed to cellular networks employing repeaters and relays.
2. Description of the Prior Art and Related Background Information
Within a wireless cellular communication network, a cell is defined by the coverage area of a base station where it can communicate successfully with a mobile user over the radio frequency (“RF”) link. As shown in FIG. 1, within the Long Term Evolution (“LTE”) network, the base station and mobile user are referred to as the evolved Node B (“eNB”) 110 and user equipment (“UE”) 120, respectively. The eNB 110 transmits signals to the UE 120 through the down-link 103, and the UE 120 transmits signals to the eNB 110 through the up-link 102. The UE 120 is operating near the cell edge 111, and is subjected to an unfavorable RF link due to distance-dependent path losses to the eNB 110. As a result, cell-edge users often experience the lowest data throughput within the cell. LTE-Advanced (release 10), an enhancement of LTE (release 8), seeks to increase the data throughput for these cell-edge users. See, for example, S. Parkvall and D. Astely, “The evolution of LTE towards IMT-advanced,” Journal of Communications, Vol. 4, No. 3, pp. 146-154, April 2009.
Repeaters and relays are employed as means for improving the link budget by reducing the distance between transmitter and receiver, which, in turn, allows for higher data rates. A repeater receives and retransmits all signals within a defined bandwidth with minimal delay. It is an amplify-and-forward device. However, repeaters amplify and generate noise in the up-link and down-link bands which is problematic for many implementations. In contrast, a relay decodes the in-coming signal, then recodes and transmits. Such devices, referred to as decode-and-forward relays, have the advantage of removing noise and interference from the desired signal. It also allows for the selection of which signals are to be relay-assisted. Unfortunately, the delay caused by the decoding and encoding processes makes it necessary for the relay to wait for the eNB scheduler to assign new radio channel resources before retransmitting the data. Therefore, relays likewise have deficiencies which are problematic in many implementations.
Accordingly, a need exists to improve cellular networks employing repeaters and relays.